Straight of grain question

I'm working on a queen size quilt and have a question on cutting the borders. I'm using the Robert Kaufman app to figure amount of fabric needed, but noticed that they show borders cut across the fabric. I thought there was a discussion about cutting border fabrics along the selvedge, rather than across, in order to have a nice flat "hang" to the quilt. Does it really matter? I'm eager to go the next step, but am concerned about how it will look when it's done. Should you go across for top and bottom, and along the length for sides?

"The business of life is making memories. In the end, it is all we have." Butler Charlie Carson, Downton Abbey, season 4, episode 3, PBS.

About the biggest practical advantage that I can think of is that you get no seams in your borders when cutting LOF (aligned with selvedge) vs. WOF (selvedge to selvedge). If your quilt is small enough that you would have no seam by cutting WOF for top/bottom and it's not too directional, you could easily do both.

Fabric has less stretch length wise, so the quilt is a bit less likely to pull out of shape while quilting if you cut the borders length of fabric. After it's quilted, I don't know as there is a difference in the drape. I let the print dictate how I'm going to handle the border fabric.

"I do not understand how anyone can live without one small place of enchantment to turn to."
Marjorie Kinnan Rawlings

I also prefer borders cut along the selvage, but.....for the times when there isn't enough fabric to do that, or the borders are pieced for whatever reason (by design or by necessity), here's a secret trick I began using many years ago to keep the outer edges from having any "give" and wave.

TWILL TAPE! Sold by the little package along with hem tape/rick rack/blanket binding at Joannes, etc.

I'm working on a queen size quilt and have a question on cutting the borders. I'm using the Robert Kaufman app to figure amount of fabric needed, but noticed that they show borders cut across the fabric. I thought there was a discussion about cutting border fabrics along the selvedge, rather than across, in order to have a nice flat "hang" to the quilt. Does it really matter? I'm eager to go the next step, but am concerned about how it will look when it's done. Should you go across for top and bottom, and along the length for sides?

I'm cheap. I refuse to buy enough fabric to cut borders along the selvage edge. When using WOF if you join the pieces with a bias seam, the seams don't show too much. And at most you'd have two joints.

I too prefer to use lenghtwise grain for borders. The wider the cut border the more the stretch becomes apparent. I have used cross grain or width of fabric , particularly for narrow borders, but I starch them so they stand up like cardboard prior to cutting.